1. Field of Invention
The present invention relates to a composition to form conductive layers included in electronic devices, an organic conductive layer including such a composition, a method to manufacture organic conductive layers, an organic EL element including the organic conductive layer, a method to manufacture organic EL elements, a semiconductor element including the organic conductive layer, a method to manufacture semiconductor elements, an electronic device, and an electronic apparatus. In particular, the above conductive layer is used as a conductive portion to form electrodes and wiring lines included in electronic circuits or integrated circuits. The composition according to the present invention can be used for raw materials for various coating processes. An inkjet process is preferably used when organic conductive layers are formed using the composition.
2. Description of Related Art
In the related art, a photolithographic process has been used for forming wiring lines included in electronic circuits or integrated circuits. In such a photolithographic process, a photosensitive material called a resist material is provided above a substrate covered with a conductive layer. A circuit pattern is irradiated and then developed. The conductive layer is then etched along the resist pattern, thereby forming wiring lines. In the photolithographic process, there is a problem in that a complicated process and a large system, such as a vacuum unit, must be used. The manufacturing cost is high because the utilization efficiency of raw materials is several percent and therefore most of the raw materials are wasted. The energy efficiency of the manufacturing process is low.
A conductive layer pattern used for the above integrated circuit or thin-film transistors contains metal, such as copper or aluminum, or indium tin oxide (ITO) and a semiconductor layer pattern used therefor contains silicon in many cases. In the related art, such patterns have been formed according to the following procedure in general. A conductive or semiconductor layer is formed over a substrate by a thermal, plasma, or optical CVD process or the like and unnecessary portions of the layer are then removed by a photolithographic process.
However, in a method for forming a thin-film pattern by a combination of the CVD process and the photolithographic process, there are the technical problems below from a process viewpoint.
(1) When a substrate on which a thin-film is formed has, for example, an irregular surface, a thin-film having a uniform thickness and uniform properties is hardly formed on the substrate because gaseous raw materials are used.
(2) The productivity is low because the rate of forming a thin-film is low.
(3) When the plasma CVD process is used, the costs of purchasing and maintaining a manufacturing apparatus are high because a complicated, expensive high frequency wave-generating and a vacuum unit are necessary.
(4) The manufacturing cost is high because the photolithographic process is complicated and the utilization efficiency of raw materials is low, and the cost of treating waste is also high because a large amount of resist materials and etching solutions are discarded.
Furthermore, in a method for forming a silicon thin-film pattern, there are the technical problems below from a material viewpoint.
(5) Raw materials are hard to handle because the raw materials contain gaseous silicon hydride having high toxicity and reactivity.
(6) In addition, a sealed vacuum unit and piping system must be used because the gaseous raw materials are used. In general, a manufacturing apparatus including such a vacuum unit and piping system is massive and such an apparatus is operated in a clean room. Hence, the maintenance cost is high.
(7) The production cost is high because the above vacuum unit and piping system are expensive and a large amount of energy is consumed in order to form a desired thin-film in such a manner that the vacuum environment and plasma environment are maintained.
In contrast, the following method has been proposed. Liquid (hereinafter referred to as a composition) containing conductive fine particles dispersed therein is applied onto a substrate by an inkjet process so as to form a pattern directly and the applied liquid is then transformed into a conductive layer pattern by thermal treatment or the application of a laser beam (see, for example, U.S. Pat. No. 5,132,248). Furthermore, the following method has been proposed. Bus and address electrodes for plasma displays are formed by an inkjet process using ink containing silver nanoparticles dispersed therein (see, for example, Tech. Digest of SID '02, pp. 753 (2002). According to these methods, the above photolithographic process is not necessary, a process for forming conductive layers can be greatly simplified, and the consumption of raw materials can be reduced. Thus, the methods are fit for manufacturing the above-mentioned electronic circuits and integrated circuits and it is expected that the methods contribute to the reduction of manufacturing cost.
However, in order to form wiring lines, the conductive fine particles must be stacked to a certain degree so as to form a thick layer. That is, if the conductive fine particles are not accumulated, portions in which the conductive fine particles are not in contact with each other cause breaks in wiring lines. If the layer thickness is insufficient, the electric resistance is high, that is, obtained wiring lines are inferior in conductivity.
In the method for directly applying the liquid containing the conductive fine particles dispersed therein onto a substrate by an inkjet process so as to form a pattern directly, the amount of the conductive fine particles provided by discharging the liquid at a constant rate is limited due to the viscosity of the discharged liquid because the liquid contains the conductive fine particles dispersed therein. When a large amount of the liquid is ejected in one shot, it is difficult to adjust positions for forming wiring lines and such wiring lines have a large width, which is not suitable for the integration of electronic circuits or the like.
The relationship between the above-mentioned inkjet process and the composition used in the process has been examined for the following technical subjects in a wide range.
(1) A method for manufacturing organic EL elements each including corresponding hole injection/transport layers formed by an inkjet process using a composition containing a polar solvent and a hole injection/transport material (see, for example, Japanese Patent Application No. 10-248816)
(2) A method in which a composition can be constantly discharged by an inkjet process and satisfactory patterning and layer-forming properties can be obtained when the composition contains an aprotic cyclic solvent, such as DMI or NMP (see, for example, Japanese Patent Application No. 11-134320)
(3) A method in which PEDOT/PSS is used as a hole injection/transport material (see, for example, Japanese Unexamined Patent Application Publication No. 2000-91081)
(4) A method in which plugging can be prevented by the use of a composition containing a glycol solvent having a high boiling temperature (see, for example, Japanese Unexamined Patent Application Publication No. 2001-167878)
(5) A method in which plugging can be prevented, the flatness of layers formed using this composition is satisfactory, and an interface can be prevented from being formed by the use of a composition containing a solvent having a predetermined volatility (vapor pressure) (see, for example, Japanese Unexamined Patent Application Publication No. 2001-52861)
In contrast, a method in which a conductive coating is formed by a screen printing process using paste has been proposed (see, for example, PCT Japanese Translation Patent Publication No. 2002-500408). Since paste has high viscosity in general, paste is not fit for an inkjet process.
On the other hand, Kawase et al. disclosed the following technique in Science: the above material PEDOT/PSS is used for forming source and drain electrodes when organic TFTs are prepared by an inkjet process (see, for example, Science, 15 Dec. 2000, Vol. 290, pp. 2123–2126).